Monitoring a subject's physiological parameters is routine in the clinic and in the hospital. Because of the interdependence of physiological and other bodily processes, monitoring of multiple related physiological parameters (referred to herein as “multiple parameter monitoring” or “MPM”) is advantageous is known in these environments.
Recent developments in sensors and sensor systems now increasingly allow single and multiple parameter physiological monitoring to move out of the controlled environments of the clinic or hospital and into less constrained environments where the subject may engage in normal activities. MPM is now possible in the subject's normal environments where the subject is carrying out normal activities with little or no constraint. “Ambulatory monitoring”, as such monitoring is known in the art, thereby encompasses the monitoring of physiological parameters during normal daily activities, including work activities, and also encompasses monitoring during unconstrained sleep. For example, during “ambulatory monitoring”, a subject may be walking, running, generally exercising, engaging in athletics, and the like; a subject may also be working at either sedentary or active tasks; a subject may also be resting, sitting, reclining, sleeping, and the like. In this application, the term “ambulatory monitoring” is used and understood to refer to monitoring physiological parameters during the broad range of subject activities, and the term “ambulatory multiple parameter monitoring” (or “ambulatory MPM”) is used to refer monitoring multiple physiological parameters during such activities.
A recent example of an ambulatory monitoring system is described in U.S. Pat. No. 6,551,252 B1, issued Apr. 23, 2003. This patent describes monitoring systems and methods comprising comfortable garments that serve as platforms for sensors of multiple physiological parameters. Ambulatory monitoring then merely requires a subject to wear such a comfortable garment.
However, processing signals recorded during ambulatory MPM signals to extract useful physiological information during is considerably often more difficult than similar processing of signals obtained during in-clinic or in-hospital monitoring. For example, characteristics such as frequency spectrum and amplitude of the signals recorded during ambulatory monitoring can vary unpredictably as the monitored subject's activity varies unpredictably. Processing must be capable of handling such unpredictable signal characteristics. In addition, unconstrained subject activities can introduce considerable artifact and noise in ambulatory monitoring signals which is also of variable characteristics. Further, non-invasive sensors usually used for ambulatory monitoring often output signals sensitive to multiple physiological systems or processes. In contrast, few is any of these problems arise during controlled in-clinic or in-hospital monitoring. Signal recording during the latter monitoring usually have only limited variability with limited artifact and noise, and sensors used can be designed for sensitivity to single physiological systems or processes.
A recent example of the complexities of ambulatory signal processing is U.S. Pat. No. 6,783,498 B2. This patent describes systems and methods for determining cardiac function from signals obtained using non-invasive sensors during ambulatory monitoring. Because the cardiac signals of interest are usually have small amplitude and are usually obscured by considerably larger amplitude respiratory and other undesired signals, careful processing is required to extract useful cardiac information.
Accordingly, the art is in need of improved processing techniques broadly applicable to signals from ambulatory MPM monitoring that provide robust and reliable extraction of useful physiological information from such signals.
A number of references are cited herein, the entire disclosures of which are incorporated herein, in their entirety, by reference for all purposes. Further, none of these references, regardless of how characterized above, is admitted as prior to the invention of the subject matter claimed herein.